1. Field of the Invention
This invention relates to an internal manifolded oxidant cooled fuel cell stack system in which the edges of the separator plates separating the fuel cell units of each of a plurality of fuel cell sub-stacks are extended to form fins. Pathways are provided for the oxidant gas to flow over the finned portions of the separator plates and into the fuel cell sub-stacks, thereby providing cooling of the fuel cell stack assembly and improved thermal management of the fuel cell stack system.
2. Description of Prior Art
In large fuel cell stack systems, internal stack cooling is a significant problem because of the impact that stack cooling has on the complexity of the stack design and balance of plant requirements. Previous attempts to provide the necessary cooling function in a large fuel cell stack system have included large high temperature oxidant flow, internal fuel reforming, or dedicated cooling plates installed throughout the stack assembly. Each of these approaches has significant technical and economic issues that must be overcome to produce a commercially viable fuel cell stack.
U.S. Pat. No. 5,230,966 to Voss et al. teaches a coolant flow field plate for electrochemical fuel cells comprising, in a major surface, a coolant inlet, a coolant outlet, at least one coolant distribution channel in fluid communication with the coolant inlet and disposed near the perimeter of the plate, and at least one central exhaust channel extending along a diagonal of the coolant flow field plate. The central exhaust channel is proximate to the center of the plate and in fluid communication with the coolant outlet. A plurality of coolant flow channels extend from the coolant distribution channels to the central exhaust channel. The coolant flow field plate is designed to increase the lifetime of solid polymer fuel cells by imposing lower temperatures near the periphery of the cell plates, thereby protecting the integrity of the seals where reactant gases are sealed against external leakage.
U.S. Pat. No. 5,514,487 to Washington et al. teaches an edge manifold assembly comprising a plurality of manifold plates which conduct, introduce and receive reactant and coolant streams to and from an electrochemical fuel cell stack. Each of the fuel cells is provided with a pair of manifold plates, each of which has at least one manifold opening formed therein for containing a fluid and at least one channel formed therein for effecting fluid communication between the manifold opening and the fuel cell to which the manifold plate is attached. The complexity of this approach in terms, for example, of the number of individual components required to make up this system will be apparent to those skilled in the art.
An example of the use of a cooling plate for internally cooling the fuel cell is taught by U.S. Pat. No. 5,344,721 to Sonai et al. This patent teaches a solid polymer electrolyte fuel cell apparatus comprising a fuel cell formed by superposing a plurality of unit cells having a solid polymer electrolyte membrane held between an anode and a cathode and cooling plate adapted to circulate a coolant throughout the interior of the fuel cell and remove the heat produced during regeneration of power. However, in order to be effective, the fuel cell apparatus requires a coolant which is a liquid having a boiling point closely approximating the working temperature of the fuel cell.
Fuel cell batteries having air conduits from a peripheral intake location to a center of the battery are taught by U.S. Pat. No. 5,264,300 to Barp et al. and U.S. Pat. No. 5,418,079 to Diethelm. U.S. Pat. No. 5,213,913 to Yamada teaches a solid electrolyte type fuel cell having gas from gas supply ducts impinging perpendicularly on electrodes.
None of these prior art references provides a solution to the problem of cooling the fuel cell while preheating the oxidant reactant gas in a manner which results in a commercially viable fuel cell stack.